Insert (Save) data in two database tables using jQuery AJAX in ASP.Net MVC

Refer below code.

Controller

public JsonResult InsertSales(SaleDetail saleDetail)
{
    using (sampledb6Entities sampledb6Entities = new sampledb6Entities())
    {
        //Check for NULL.
        if (saleDetail.sales == null)
        {
            //Loop and insert records.
            foreach (Sale sale in saleDetail.sales)
            {
                sampledb6Entities.Sales.Add(sale);
            }
        }

        //Check for NULL.
        if (saleDetail.saleItems == null)
        {
            //Loop and insert records.
            foreach (SaleItem saleItem in saleDetail.saleItems)
            {
                sampledb6Entities.SaleItems.Add(saleItem);
            }
        }

        int insertedRecords = sampledb6Entities.SaveChanges();
        return Json(insertedRecords);
    }
}

public class SaleDetail
{
    public List<Sale> sales { get; set; }
    public List<SaleItem> saleItems { get; set; }
}

View

<table id="table" class="table">
    <thead>
        <tr>
            <th scope="col">Product Id</th>
            <th scope="col">Company</th>
            <th scope="col">Product Name</th>
            <th scope="col">User Name</th>
            <th scope="col">User Mobile</th>
            <th scope="col">Price per product</th>
            <th scope="col">Quantity</th>
            <th scope="col">Total Price</th>
        </tr>
    </thead>
    <tbody></tbody>
    <tfoot>
        <tr>
            <td colspan="2">Grand Total : </td>
            <td id="GrandTotal"></td>
        </tr>
    </tfoot>
</table>
<script>
    $('#productSelect').change(function () {
        var id = $(this).val();
        if (id > 0) {
            $.get("GetProduct", { productId: id }, function (result) {
                console.log(result)
                $("tbody").append("<tr><td>" + result.ProductId + "</td><td>"
                    + result.CompanyName + "</td><td>"
                    + result.ProductName + "</td><td>"
                    + result.UserName + "</td><td>"
                    + result.UserMobile + "</td><td>"
                    + result.ProductPrice + "</td><td>"
                    + "<button type='button' class='btn btn-primary' onClick='subtract(" + id + "," + result.ProductPrice + ")'>-</button><button type='button' class='btn btn-dark'  id='" + id + "' value='0'>0</button><button type='button' class='btn btn-primary' onClick='add(" + id + "," + result.ProductPrice + ")'>+</button></td><td id='sum" + id + "'>0</td><td><a onclick='removeRow(this)'>x</a></td></tr>")
                CalculateGrandTotal();

            });
        }
    })

    $("body").on("click", "#btnSave", function () {
        //Loop through the Table rows and build a JSON array.
        var saleDetail = {};
        var sales = new Array();
        var saleItems = new Array();
        $(".table tbody tr").each(function () {
            var row = $(this);
            var Sale = {};
            Sale.UserName = row.find("td").eq(3).html();
            Sale.UserMobile = row.find("td").eq(4).html();
            Sale.NetTotal = row.find("td").eq(8).html();
            Sale.ProductQuantity = row.find("td").eq(5).val();
            sales.push(Sale);

            var SaleItems = {};
            SaleItems.ProductId = row.find("td").eq(0).html();
            SaleItems.Quantity = row.find("td").eq(6).html();
            SaleItems.ProductName = row.find("td").eq(2).val();
            saleItems.push(SaleItems);
        });

        saleDetail.sales = sales;
        saleDetail.saleItems = saleItems;

        $.ajax({
            type: "POST",
            url: "/Product/Insertsales",
            data: JSON.stringify(saleDetail),
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function (r) {
                alert(r + " records inserted.");
            }
        });
    });
</script>